1. Field of the Invention
This invention relates to furnaces used to heat structures and is particularly applicable to furnaces used to heat residential structures.
With the increase in the cost of fuel, particularly petroleum-based fuel, as well as the uncertainty of its uninterrupted availability from foreign sources, there is increasing concern for obtaining the maximum possible efficiency from residential heating systems. In the past, approximately 25% of the heat produced when the furnace was running escaped up the chimney rather than being transferred to the house. In addition, when the furnace is turned off, drafts through the furnace continue to pull warm air up the chimney and out of the house, usually from the basement where most furnaces are located in family residences. This loss due to chimney draft while the furnace is off accounts for an additional 25% loss of the heat produced.
A number of electrically operated flue dampers which depend upon electrical switching and safety relays to assure operation when the furnace is turned on and to power it closed have been put on the market in recent years. Obviously, such devices present safety hazards, and their cost is very significant to the average homeowner.
The present invention is directed to an efficient flue damper for preventing heat loss up the chimney when the furnace is in the off condition and also serves to minimize the heat loss during operation of the furnace.
2. Prior Art
U.S. Pat. No. 1,743,731 Scott discloses a flue damper consisting of a pair of plate wing members positioned within the smoke pipe which are pushed open when the furnace is on but fall into a closed position through gravity when the furnace is off. They are positioned along an oblique horizontal axis in the horizontal flue.
U.S. Pat. No. 1,830,575 Tjernblom discloses a damper for supplying the air to the fire pot from a blower. In this case, the damper closes to prevent a natural draft of the fire by preventing the chimney from drawing in an oversupply of air to the fire pot. The damper is comprised of two horizontally pivoted flappers, the upper of which overlaps the pivot of the lower.
Another approach is illustrated in U.S. Pat. No. 2,557,210 Viola, et al wherein a horizontally pivoted flapper valve with a weight control is utilized. In this case, an adjustment is utilized so that the damper will just close when there is no fire in the furnace and the damper will open with a very light draft.